Example code for connecting to and using a postgres database using discord.py and asyncpg.

example_db.py

# asyncpg docs: https://magicstack.github.io/asyncpg/current/

# This uses discord.py rewrite branch and .format(). If you are using the async branch of discord.py, it shouldn't matter much
# as only 'await ctx.send()' is something you should need to change. If you are using python 3.6+, you can use f strings as opposed to
# .format() for increased efficiency.

import discord
from discord.ext import commands
import asyncio
import asyncpg

async def run():
    description = "A bot written in Python that uses asyncpg to connect to a postgreSQL database."

    # NOTE: 127.0.0.1 is the loopback address. If your db is running on the same machine as the code, this address will work
    credentials = {"user": "USERNAME", "password": "PASSWORD", "database": "DATABSE", "host": "127.0.0.1"}
    db = await asyncpg.create_pool(**credentials)

    # Example create table code, you'll probably change it to suit you
    await db.execute("CREATE TABLE IF NOT EXISTS users(id bigint PRIMARY KEY, data text);")

    bot = Bot(description=description, db=db)
    try:
        await bot.start(config.token)
    except KeyboardInterrupt:
        await db.close()
        await bot.logout()

class Bot(commands.Bot):
    def __init__(self, **kwargs):
        super().__init__(
            description=kwargs.pop("description"),
            command_prefix="?"
        )

        self.db = kwargs.pop("db")

    async def on_ready(self):
        # .format() is for the lazy people who aren't on 3.6+
        print("Username: {0}\nID: {0.id}".format(self.user))

    # Example commands, don't use them
    # Don't even use this format, this is not an example of how to make commands.
    @commands.command()
    async def query(ctx):
        query = "SELECT * FROM users WHERE id = $1;"

        # This returns a asyncpg.Record object, which is similar to a dict
        row = await bot.db.fetchrow(query, ctx.author.id)
        await ctx.send("{}: {}".format(row["id"], row["data"]))

    @commands.command()
    async def update(ctx, *, new_data: str):
        # Once the code exits the transaction block, changes made in the block are committed to the db

        connection = await bot.db.acquire()
        async with connection.transaction():
            query = "UPDATE users SET data = $1 WHERE id = $2"
            await bot.db.execute(query, new_data, ctx.author.id)
        await bot.db.release(connection)

        await ctx.send("NEW:\n{}: {}".format(ctx.author.id, new_data))

loop = asyncio.get_event_loop()
loop.run_until_complete(run())